Polyethylene terephthalate (“2GT”) and polybutylene terephthalate (“4GT”), generally referred to as “polyalkylene terephthalates”, are common commercial polyesters. Polyalkylene terephthalates have excellent physical and chemical properties, in particular chemical, heat and light stability, high melting points and high strength. As a result they have been widely used for resins, films and fibers, including staple fibers and fiberfill comprising such staple fibers.
Polytrimethylene terephthalate (3GT) has achieved growing commercial interest as a fiber because of the recent developments in lower cost routes to 1,3-propane diol (PDO), one of the polymer backbone monomer components. 3GT has long been desirable in fiber form for its disperse dyeability at atmospheric pressure, low bending modulus, elastic recovery and resilience. In many end-uses, such as fiberfill applications, staple fibers are preferred over continuous filament.
The manufacture of staple fiber suitable for fiberfill poses a number of potential advantages as well as some specific problems over prior staples used in fiberfill. The challenges lie in obtaining a balance of properties which includes obtaining satisfactory fiber crimp, and sufficient fiber toughness (breaking strength and abrasion resistance), while preserving the softness and low fiber-to-fiber friction. This balance of properties is essential to achieve both downstream processing such as carding or garnetting, while ultimately providing a desirable consumer product.
In the case of 2GT, which is a widely used staple fiber for fiberfill, these problems are being met by the fiber producers through improvements in polymerization chemistry and optimized fiber production. This has led to improved spinning and drawing processes tailored to the production of high performance 2GT fibers. There is a need for an improved 3GT staple fiber process which generates fibers with suitable processability in commercial mills employing carding and garnetting processes. The solutions to these problems developed over the years for 2GT or 4GT fibers frequently do not directly translate to 3GT fibers because of the unique properties inherent in the 3GT polymer chemistry.
Downstream processing of staple fibers into fiberfill end uses is typically done on conventional staple cards or garnets. The carded web or batt is typically cross-lapped to a desired basis weight and/or thickness, optionally bonded, and then directly inserted as the filling material in the desired end use. In the case of pillows for use in sleep comfort, the batt (which may be optionally bonded by incorporation of a resin or lower melting fiber and passage of the batt through a heated oven) is cut and filled into a pillow ticking at a typical loading of 12-24 ounces. As outlined above, this process includes several steps, many of which are done at high speeds and subject the fibers to a significant amount of abrasion, placing demands on the fiber tensile properties. For example, the initial step is fiber opening, which is often done by tumbling the fibers on motorized belts which contain rows of pointed steel teeth for the purposes of pulling and separating large group of fibers. The opened fibers are then conveyed via forced air and, typically, are then passed thorough networks of overhead ductwork or chute feeders. The chute feeders feed the card or garnett, devices which separate the fibers via the combing action of rolls containing a high density of teeth made of rigid wire.
The fibers must possess a critical set of physical properties such that they will pass through the above process with efficiency (minimal fiber damage and stoppages), while making a material suitable for use as a fiberfill. One of the most critical parameters is fiber strength, defined as the tenacity or grams of breaking strength per unit denier. In the case of 2GT, fiber tenacities of 4 to 7 grams per denier are obtainable over a wide range of fiber deniers. In the case of 3GT, typical tenacities are below 3 grams per denier. These fibers with only a few grams of breaking strength are not desirable for commercial processing. There is a need for 3GT staple fibers with tenacities over 3 grams per denier, especially for fibers on the lower denier end of the typical range for fiberfill staples (2.0-4.5 dpf). Additionally, Crimp take-up, a measure of the springiness of the fiber as imparted by the mechanical crimping process, is an important property for fiberfill staples, both for processing the staple fibers and for the properties of the resulting fiberfill product. Further fiber modifications typically include application of a coating to tailor the fiber surface properties to increase the loft or refluffability of the structure, as well as to reduce the fiber-to-fiber friction. These coatings are typically referred to as “slickeners”. Such coatings allow easier motion amongst the fibers as described by U.S. Pat. Nos. 3,454,422 and 4,725,635. The coatings also increase the overall deflection of the assembly, since fibers would slide easier over each other.
Fiber crimp also influences the load bearing performance of the three dimensional structure. Fiber crimp, which may be two-dimensional or three dimensional, is conventionally produced via mechanical means or it may be inherent in the fiber due to structural or compositional differences. Assuming constant fiber weight, similar fiber size, geometry and surface properties, in general a lower crimp fiber (i.e., a high amplitude, low frequency crimp) will produce higher loft (i.e., a high effective bulk, low density three dimensional structure, which will deform easily under a given standard load due to low level of interlocking of the crimped fibers). In contrast, higher crimp fibers (low amplitude, high frequency) generally produce three dimensional structures with higher density and reduced loft. Such higher density three dimensional structures will not deform as readily when a standard load is applied, due to a higher level of fiber interlocking in the structure. In typical filled articles, the applied load (i.e., the load the article is designed to support) is high enough to cause relative displacement of fibers in the structure. However, this load is not high enough to cause plastic deformation of the individual fibers.
The crimp level also affects the fiber's ability to recover from compression. Low crimp level fibers do not recover as readily as high crimp fibers since low crimp fibers lack the “springiness” that higher crimp provides. On the other hand, low crimp fibers are easier to refluff due to the lower amount of fiber interlocking. As discussed above, the user of the filled article typically wants both support and loft. Both of these properties are greatly influenced by crimp frequency, but in opposite and conflicting ways. To get high loft, one uses low crimp. Conversely, to get high support, one uses high crimp. Additional variables one may modify include altering the mechanical properties of the fiber, adjusting the fiber denier, and/or manipulating the fiber cross-section.
For end use applications of fiberfill staple, the product must meet several criteria which are requisite to nearly all commercial applications. There is a need for high bulk, especially effective and resistive bulk. Effective bulk means the filling material fully and effectively fills the space in which it is placed. Materials having a high level of effective bulk are said to have good “filling power” because of their ability to provide a high crown or plump appearance to the filled article. Resistive bulk, also herein referred to as “support bulk,” means the filling material resists deformation under an applied stress. Structures with resistive bulk filling will not have a pad-like feeling under load and will provide some measure of resilience support even under high stresses. Resistive bulk filling is desirable because filled articles provide both good support bulk and are highly insulative.
Resilience, i.e., recovery from tension or compression, is another important characteristic for filling material. Materials with high resilience are lively and exhibit a significant degree of recovery from tension or compression, while low resilience materials are less springy. Resilience and support are especially important for materials used in products such as pillows, which must yield to conform to the shapes of any objects applying compression and at the same time provide adequate support for the objects. Additionally, once the object is removed, the pillow must recover from the compression and be ready to conform and support subsequent objects placed thereon. Finally, as resilience increases, the commercial processability of fibers improves.
Traditionally, down filling material was used in products to provide cushioning and insulation in addition to softness to the touch desirable in many applications. However, major drawbacks to traditional filling material include its high cost and the allergens commonly found in the down material. Additionally, because down filling material is not waterproof, it absorbs water and becomes heavy and provides less cushioning support when exposed to wet environments.
The art of producing and perfecting synthetic fiberfill materials seeks to solve these and other problems. The ultimate goal in this area has been to produce synthetic fiberfill as resilient, comfortable and refluffable as down but at the same time, providing the two key advantages over down: a hypoallergenic and waterproof filling. A major advancement was introduction of synthetic fiberfill material made from polyesters. 2GT has long been used to produce fiberfill material having some of the qualities of down. Throughout the years, many researchers have sought to create polyester fiberfill material approaching down by emulating its form or finding ways to approximate its performance. Methods of creating new structures or fiber shapes are described in Marcus, U.S. Pat. Nos. 4,794,038 and 5,851,665, Broaddus, U.S. Pat. No. 4,836,763, and Samuelson, U.S. Pat. No. 4,850,847. However synthetic polyesters made from such polyesters have shortcomings in that 2GT polyester fibers are inherently rigid, and have high fiber-to-fiber friction. This latter property which even for fibers treated with a cureable silicone finish, causes the fibers to become matted and clumped together due to fiber entanglement and abrasion. Presumably these phenomena cause the slickener coating to be damaged or removed over the life of the fiberfill.
Fibers in fiberfill applications are combined to form three-dimensional (“3D”) load-bearing structures. The load-deflection characteristics of such three dimensional structures are influenced by three key factors: the properties of the fiber making up the structure; the manufacturing technique used to make the three dimensional structure; and the enclosure surrounding the three dimensional structure. Moreover, studies have indicated that the deflection of such a structure is due to the displacement of individual fibers in the structure. Fiber displacement in such structures is dependent on the amount of crimp on each fiber (which affects the amount of interlocking), the mechanical properties (i.e., bending moment and Young's Modulus), the fiber's recovery properties (how easily the fibers can be deflected and how easily they recover from that deflection), the fiber's size and geometry, and the fiber-to-fiber friction properties of the fibers (how easily fibers slide over each other).
While commercial availability of 3GT is relatively new, research has been conducted for quite some time. For instance, U.S. Pat. No. 3,584,103 describes a process for melt spinning 3GT filaments having asymmetric birefringence. Helically crimped textile fibers of 3GT are prepared by melt spinning filaments to have asymmetric birefringence across their diameters, drawing the filaments to orient the molecules thereof, annealing the drawn filaments at 100-190° C. while held at constant length, and heating the annealed filaments in a relaxed condition above 45° C., preferably at about 140° C. for 2-10 minutes, to develop crimp. All of the examples demonstrate relaxing the fibers at 140° C.
JP 11-107081 describes relaxation of 3GT multifilament yarn unstretched fiber at a temperature below 150° C., preferably 110-150° C., for 0.2-0.8 seconds, preferably 0.3-0.6 seconds, followed by false twisting the multifilament yarn.
EP 1 016 741 describes using a phosphorus additive and certain 3GT polymer quality constraints for obtaining improved whiteness, melt stability and spinning stability. The filaments and short fibers prepared after spinning and drawing are heat treated at 90-200° C.
JP 11-189938 teaches making 3GT short fibers (3-200 mm), and describes a moist heat treatment step at 100-160° C. for 0.01 to 90 minutes or dry heat treatment step at 100-300° C. for 0.01 to 20 minutes. In Working Example 1, 3GT is spun at 260° C. with a yarn-spinning take-up speed of 1800 m/minute. After drawing the fiber is given a constant length heat treatment at 150° C. for 5 minutes with a liquid bath. Then, it is crimped and cut. Working Example 2 applies a dry heat treatment at 200° C. for 3 minutes to the drawn fibers.
British Patent Specification No. 1 254 826 describes polyalkylene filaments, staple fibers and yarns including 3GT filaments and staple fibers. The focus is on carpet pile and fiberfill. Example IV describes the use of the process of Example I to prepare 3GT continuous filaments. Example V describes use of the process of Example I to make 3GT staple fibers. Example I describes passing a filament bundle into a stuffer box crimper, heat setting the crimped product in tow form by subjecting it to temperatures of about 150° C. for a period of 18 minutes, and cutting the heat-set tow into 6 inch staple lengths. Example VII describes the testing of 3GT staple fiberfill batts comprising 3GT prepared according to the process of Example IV.
All of the documents described above are incorporated herein by reference in their entirety.